Preform and method for reinforcing woven fiber nodes

ABSTRACT

Preforms including fiber reinforced nodes for use in fiber reinforced composite structures and methods for making fiber reinforced composite structures. Preforms with woven fabric elements extending radially from a common node include at least one reinforcing fiber interwoven between at least two elements and passing through the node. A method of assembling preform structures using the preforms to provide a structure with reinforced nodes.

FIELD OF THE INVENTION

The present invention relates to fiber-reinforced structures. Morespecifically, the present invention relates to fiber reinforced preformswith planar components intersecting along an edge of at least one of thecomponents. More specifically still, the present invention relates to amethod of fabricating woven preforms having fiber reinforced nodes orjoints and structures fabricated from such a method. The method may beused in the fabrication of preforms for the production of grid-likestructures.

BACKGROUND OF THE INVENTION

Fiber reinforced composite structures often require two or more elementsto be joined along an edge of at least one of the elements to form ajoint, or node. For example, a structure may have fiber reinforced wovenplanar elements arranged at intersecting angles such that the elementsintersect along an edge of at least one of the elements. A structure mayinclude planar non-woven elements, for example metal sheets or plates,or ceramic panels or panels of other composition, which intersect alongat least one edge.

Joining of intersecting elements may be useful in the production ofgrid-like structures or composite panels or skins with reinforcing ribs.In such cases, it may be desirable or necessary to provide a jointbetween the elements along the line of intersection. One method ofachieving such a joint is to form the second element to be joined to afirst element longer than necessary. The excess material of the secondelement is folded parallel to and placed adjacent to the first elementsuch that a portion of the second element overlaps a portion of thefirst element to form a single lap joint with the overlapping portions.The overlapping portions may be fixed to each other by mechanical means,such as threaded fasteners or rivets, or chemical means, such asadhesives or resins as known in the art. Many typical applications relyupon adhesives or resins to fix the elements together.

In some cases, the second element assumes a general L-shape with one legof the L (either the vertical or horizontal leg) parallel and adjacentto the first element. In forming a grid-like structure, a series ofintersecting first and second elements can be formed as described aboveto form the desired grid-like structure. In some grid-like structures,first elements may be arranged in parallel rows with intersecting secondelements arranged as required. Between adjacent first elements, thesecond elements may take on a general C-shape with approximately linearand parallel top and bottom segments, and a middle segment between, andmutually perpendicular to, the top and bottom segments. A similar resultmay be obtained with a second element in a general Z-shape withapproximately linear top and bottom segments parallel to each other andperpendicular to a generally linear middle segment. In some cases, themiddle segment may not be perpendicular to the top and bottom segments.In either form, the top and bottom segments of the second element can befixed to adjacent first elements forming a grid-like structure.

According to known methods, the node or joint between the first andsecond elements is formed by a single lap shear joint parallel to thefirst elements. The single lap shear joint provides the structuralintegrity of the node with the strength of the node reliant upon themeans used to join the first and second elements. Loads transferred fromone element to another through the node necessarily go through the jointbetween the elements.

A drawback associated with nodes formed by single lap shear joints isthat the strength of the joint is determined by the strength of the lapjoint between the overlapping portions. Because the elements remainstructurally separate, stresses applied to, or transferred to, theintersections are typically carried by the adhesive alone. The strengthof the joint therefore depends on the strength of the adhesive, which inmost cases is less than the strength of the fiber-reinforced elements.The difference in strength may be significant. Joints relying onadhesive alone are often the weak point in the structure.

In addition to poor strength at the nodes, present methods forfabricating a grid-like structure require significant manual labor inplacing individual pieces of woven fabric in a mold, and wrappingportions of the mold with the fabric to form the open cell portion ofthe grid.

The present invention addresses the shortcomings of the prior art byproviding a preform comprising a reinforced node and a method offabricating a composite structure with a reinforced joint or nodebetween elements using the claimed preform. The invention also providesa method of fabricating grid-like structures with reinforced nodes thatis both less labor intensive and costly than prior methods.

Citation or identification of any document in this application is not anadmission that such a document is available as prior art to the presentinvention.

SUMMARY OF THE INVENTION

According to aspects of this invention, a woven preform is presentedcomprising multiple legs interwoven through a common line ofintersection, the line of intersection forming a reinforced node orjoint. (For purposes of this description, “node” and “joint” are usedinterchangeably unless the context indicates otherwise.) The legs may becommonly woven and arranged substantially radially around, and directedoutwardly from, the node. The preform may include a dry fiber preformthat is united with other dry preforms and converted into a compositestructure using known techniques, such as resin transfer molding. Thepreform may also include pre-impregnated fabric that may be united withanother fabric or fabrics and cured to form a composite structure. Thepreform may also include a cured composite element that can be bonded toother composite elements to form a composite structure.

According to embodiments of this invention, a reinforced node includingone or more fibers interwoven between two or more legs and woven throughthe node or joint is formed. The preforms may be useful in fabricating,among other things, grid-like structures which could, for example, beused as thrust reverser vanes, or cascades, as may be found in gasturbines used in the aerospace industry. The preforms may also be usefulin fabricating reinforced composite panels or skins. Other applicationswould be obvious to one of ordinary skill in the art.

According to an exemplary embodiment of the invention, a woven preformcomprising a plurality of legs interwoven through a common line ofintersection forming a reinforced joint or node is provided. Wovenpreforms according to this non-limiting example may be joined with othersimilar preforms to form a grid-like structure with reinforced joints ornodes. By placing a portion of one or more legs from a first preformparallel and adjacent to, and in abutting contact with, a portion of oneor more legs from a second similar preform, and repeating the pattern, agrid-like structure may be formed with reinforcing fibers runningthrough the node and legs from adjacent preforms joined together.

According to some embodiments, at least one of the legs may be ofuniform thickness along its length taken from the common node to thefree end of each leg. In other embodiments, at least one side of atleast one leg may be tapered along its length from the common node tothe free end or tip of the leg. In still other embodiments, both sidesof at least one leg may be tapered along the length of the leg from thecommon node to the free end or tip of the leg.

In a non-limiting example, a conventional loom may be used to produce afirst elongate preform having four commonly woven elements or legsarranged in a cruciform shape when viewed perpendicular to the length(i.e., along the longitudinal axis). A second similarly sized and shapedpreform may be produced separately or cut from the first preform. Thetwo preforms may be arranged with the longitudinal axes generallyparallel and oriented such that one leg or element of the first preformis parallel to a leg or element of the second preform and the parallelelements are at least partially overlapping and abutting. In such anarrangement, the two cruciform preforms are configured such that fourelements are parallel and generally coplanar. These may be represented,for example, as the horizontal elements of the two cruciform preforms.

The other two elements of each preform are perpendicular to the coplanarelements, parallel to each other and spaced apart. In this example,these would be represented by four vertical elements.

Together, the two cruciform preforms comprise a composite structurefirst subassembly.

A second subassembly, similarly sized, shaped, and configured, can bepositioned such that two of the vertical elements of the secondsubassembly at least partially overlap and abut two vertical elements ofthe first subassembly. Thus placed together, four cruciform preformsform one complete (center) cell of a 3×3 grid. In this example, the gridmay resemble a tic-tac-toe grid. The perimeter grid cells areincompletely closed, with the corner cells having two sides in place andthe four internal cells having three sides in place. From this basicconfiguration, additional cruciform preforms can be added to enclose atleast some of the partially formed cells to increase the size of thegrid as desired.

The preform grid can subsequently be processed into a compositestructure through known methods depending upon the composition of thepreform. For example, if the preform is comprised of dry fibers, aprocess such as resin transfer molding may be used to introduce a resinto the preform and cured to form a composite structure. A preformcomprised of pre-impregnated components may be co-cured underappropriate conditions to bond the preforms to form a compositestructure. A grid assembled from fully cured composite components may beformed into a composite structure by providing an appropriate bondingmaterial to the overlapping portions of the elements and curing thebonding material. Other known methods of composite structureconstruction may be used depending on the preform composition,requirements of the composite structure, or other concerns.

According to other non-limiting examples, a first elongate preformhaving fewer than four elements, for example three elements, or morethan four elements, for example five elements may be formed. In someinstances, a conventional loom may be used to produce the woven fabricfor the preforms. In some embodiments, the preforms, when viewed in across section perpendicular to the length, would have a common,centrally located node from which each of the elements extends radially.

Preforms may be linear in the length dimension or may be curvilinear.Linear preforms would yield a linear node, while a curvilinear preformwould yield a node with a curvature in one or more directions whenviewed along the intersection. Either shape preform can be assembled toform a grid-like structure using similar processes.

Another exemplary embodiment of the present invention is directed to areinforced preform comprising interwoven legs arranged in pairs ofadjacent legs having a common line of intersection and commonly wovenreinforcement, forming a reinforced node. The multiple leg pairs may bewoven such that reinforcing fibers are woven between the individual legsin a pair as well as between one or more additional legs or leg pairs.The node is formed between the interwoven leg pairs at the common lineof intersection and includes reinforcing fibers interwoven between thelegs.

The leg pairs may be substantially planar and parallel, spaced apartfrom each other forming a void, and configured to accept a planarelement in the void formed between the legs. For purposes of thisdisclosure, an “element” can be a woven fabric or woven fabric structurethat is combined with other woven fabric components, elements, orpreforms, through known processes, to form a composite structure, ornon-woven structures such as metallic sheets or plates, or panels, suchas ceramic panels, or panels of other material. If woven, “elements” maybe dry fiber fabrics or preforms, pre-impregnated fabrics or preforms,cured composite elements, or of other known compositions depending onthe particular use and stage in the manufacturing process.

For example, a preform having six legs arranged in three pairs ofadjacent legs may accept three planar elements, one between each pair oflegs. In this non-limiting example, the preform provides the threeplanar elements intersecting at a joint, or node, with fiberreinforcement through the node. Similarly, eight legs arranged in fourpairs of legs could accept four elements. The leg pairs may be spacedequidistant around the node or may be unevenly spaced as required.

In a similar fashion, the leg pairs may be substantially non-planar withlocally parallel facing surfaces, spaced apart from each other forming avoid, and configured to accept a similarly shaped non-planar element inthe void formed between the legs. At least the inner facing surfaces ofthe two legs in a pair have generally matching, but opposite, contours.That is, if the inner facing surface of a first leg is concave at aparticular point, a corresponding location on the inner facing surfaceof the second leg would have a curvature similar in degree but oppositein sense, meaning convex at that point. Thus, parallelism, or nearparallelism, between inner facing surfaces of the legs in a pair issubstantially maintained at all points.

For a non-limiting example, in a woven fabric element having twoparallel major surfaces (as opposed to edge surfaces), the majorsurfaces may have a simple, varying, or complex curvature, where thecurvature of one side of the fabric is the inverse of the other side,maintaining localized parallelism of element faces. That is, if onesurface has a concave curvature at a particular location, thecorresponding location on the opposite side of the fabric necessarilyhas a convex curvature. The element may have constantly changingcurvatures over the surface of the fabric.

A leg pair configured to receive a portion of a non-planar element wouldhave a contour and configuration substantially the same as the portionof the element to be received. When such curvilinear preforms areassembled, the legs in the preform structure would have curved lines ofintersection, with curvature in one or more directions.

Regardless of the planarity of the elements and leg pairs, a preformstructure comprising one or more preform leg pairs and one or moreelements can be processed into a composite structure using methodssimilar to those discussed above. The leg pairs and associated elementsmay be cured, co-cured, or bonded to produce a composite structure. Theinterface between the preform and element may comprise a single ordouble lap shear joint.

According to embodiments of the inventive method, a process is disclosedin which grid-like structures can be fabricated with reinforced nodes ina more economical process than previously known. The method is suitablefor use with shaped preforms as discussed above, that is, the preformsmay have a cruciform shape when viewed along their length, and thelength may be linear or curvilinear. The process may include a mold orform (typically referred to as a “tool” or “tooling”) shaped andconfigured to correspond with the desired shape of the finished product.

Preforms according to the invention may be fabricated from fibers thathave a coating capable of being cured. Alternately, a suitable coatingmay be added to the preform prior to fabrication of the grid-likestructure. Non-limiting examples of preforms capable of being curedinclude preforms woven from fibers coated with sizing or tackifiersprior to weaving, tackifiers applied to the preform after weaving, andpreforms pre-impregnated with a resin material.

Preforms may be used as inserts in an appropriately sized and shapedmold. The inserts to be used may be cut to near net shape prior toinsertion in the mold, or they may be trimmed while in the mold. In themold, the inserts may be placed in appropriately shaped cavitiesprovided within the tool or mold with portions of adjacent preformsoverlapping and abutting each other.

Additional materials may also be placed within the mold as required. Themold, preforms, and any additional inserted material may be pre-heatedin the mold. A resin or matrix material may be injected underappropriate conditions, including pressure and temperature, to solidifythe grid-like structure. After proper processing, the grid-likestructure may be removed from the mold and trimmed to final size asnecessary.

According to embodiments of this invention, a reinforced preform isprovided comprising a plurality of commonly woven fabric elementsedgewise joined and radially extending from a common node wherein atleast one reinforcing fiber from each of the plurality of elements iswoven through the node and into at least one other of the plurality ofelements. In some embodiments, at least one of the fabric elementscomprises generally parallel major surfaces. In other embodiments, atleast one of the major surfaces tapers from the node to the end of theelement. In some embodiments, the fabric elements are arranged in pairsof adjacent elements such that opposite facing adjacent major surfacesof the elements are spaced apart a distance and form a voidtherebetween.

In some embodiments of the invention, a composite structure, orgenerally a structure, is provided which comprises a plurality ofpreforms each of which comprises a plurality of commonly woven fabricelements edgewise joined and radially extending from a common node withat least one reinforcing fiber from each of the plurality of elementswoven through the node and into at least one other of the plurality ofelements. Each of the plurality of preforms includes a longitudinalaxis, and the preforms are arranged such that the axes are alignedgenerally parallel in a grid-like pattern. A first end of a woven fabricelement overlaps and abuts at least a first woven fabric element.

In embodiments of the structure, provided are elements which comprisemajor surfaces wherein at least a first of the plurality of preformscomprises adjacent elements arranged in pairs such that opposite facingadjacent major surfaces are spaced apart a distance and form a voidtherebetween. An element is provided which is at least partiallyreceived within the void, overlapping and abutting at least a portion ofone of the opposite facing adjacent major surfaces thereof. In someembodiments, a second preform of the plurality of preforms comprisesadjacent elements arranged in pairs such that opposite facing adjacentmajor surfaces are spaced apart a distance and form a void therebetween.A second end of the element is at least partially received within thevoid formed in the second preform, overlapping and abutting at least oneof the opposite facing adjacent major surfaces thereof.

Embodiments of a method of forming a reinforced composite structureinclude fabricating a first reinforced preform comprising a plurality ofcommonly woven fabric elements edgewise joined and radially extendingfrom a common node wherein at least one reinforcing fiber from each ofthe plurality of elements is woven through the node and into at leastone other of the plurality of elements; fabricating a second reinforcedpreform like the first comprising at least one element; positioning atleast a portion of the element adjacent to at least a portion of thefirst woven preform to form a preform assembly; processing the preformassembly to form a composite structure.

In some embodiments of the inventive method, the fabric elements of thefirst woven preform comprise major surfaces. In other embodiments, thesecond reinforced preform further comprises a plurality of commonlywoven fabric elements, comprising major surfaces, edgewise joined andradially extending from a common node wherein at least one reinforcingfiber from each of the plurality of elements is woven through the nodeand into at least one other of the plurality of elements. Inembodiments, the first and second reinforced preforms have longitudinalaxes and are arranged with their longitudinal axes generally parallel.The first and second preforms are assembled such that a portion of atleast one of the major surfaces of the first woven preform at leastpartially overlaps and abuts a portion of at least one of the majorsurfaces of the second woven preform.

Some embodiments of the method include arranging at least some of thefabric elements of a first preform in pairs of adjacent elements suchthat opposite facing adjacent major surfaces are spaced apart a distanceand form a void therebetween; and positioning at least a portion of thefirst end of the element of a second preform within one of the voidsformed in the first reinforced preform, overlapping and abutting atleast a portion of one of the opposite facing adjacent major surfacesthereof.

Other embodiments include arranging at least some of the fabric elementsin pairs of adjacent elements such that opposite facing adjacent majorsurfaces are spaced apart a distance and form a void therebetween;positioning a first end of a woven element such that it is at leastpartially received within the void formed in the first reinforcedpreform; and positioning a second end of the element such that it is atleast partially received in one of the voids formed in the secondreinforced preform, overlapping and abutting at least a portion of oneof the opposite facing adjacent major surfaces thereof.

It is noted that in this disclosure and particularly in the claims,terms such as “comprises,” “comprised,” “comprising” and the like canhave the meaning attributed to it in U.S. Patent law; e.g., they canmean “includes,” “included,” “including” and the like.

These and other embodiments are disclosed or are apparent from andencompassed by the following Detailed Description.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description, given by way of example and notintended to limit the invention to the disclosed details, is made inconjunction with the accompanying drawings, in which like referencesdenote like or similar elements and parts, and in which:

FIG. 1 is a perspective view of a grid-like structure;

FIG. 2 is a perspective view of a reinforced panel or skin;

FIGS. 3 a-3 c are axial views of elements which may be used in thegrid-like structure of FIG. 1 or the reinforced panel of FIG. 2;

FIG. 4 is an axial view of a woven reinforced preform according to anembodiment of the invention;

FIG. 5 is an axial view of a woven reinforced preform according to anembodiment of the invention;

FIG. 6 is an axial view of a woven reinforced preform according to anembodiment of the invention;

FIG. 7 is an axial view of a woven reinforced preform according to anembodiment of the invention;

FIG. 8 is a perspective view of a woven reinforced preform according toan embodiment of the invention;

FIG. 9 is a plan view of a reinforced woven preform structure accordingto an embodiment of the invention;

FIG. 10 is a plan view of a reinforced woven preform structure accordingto an embodiment of the invention;

FIG. 11 is a plan view of a reinforced preform structure according to anembodiment of he invention;

FIG. 12 is a perspective view of a grid-like structure made according toan embodiment of the invention;

FIG. 13 is a perspective view of mold elements retaining and shaping areinforced woven preform prior to formation of a composite structure;

FIG. 14 is a perspective view of a composite structure produced by themold elements and preform of FIG. 13;

FIG. 15 is a reinforced structure according to an embodiment of theinvention;

FIG. 16 is an axial view of a reinforced woven preform according to anembodiment of the invention; and

FIG. 17 is a plan view of a reinforced woven preform structurecomprising the woven reinforced preform of FIG. 16.

DETAILED DESCRIPTION

Embodiments of the invention are described below with reference to theaccompanying drawings which depict embodiments of woven reinforcingpreforms and composite structures produced therefrom. However, it is tobe understood that application of the invention encompasses otherreinforcing preforms and is not limited to those illustrated. Also, theinvention is not limited to the depicted embodiments and the detailsthereof, which are provided for purposes of illustration and notlimitation.

Composite structures often include details that require elements to bejoined along their edges. FIG. 1 illustrates an open grid-like compositestructure 1 including woven first elements 10 intersecting with, andjoined to, woven second elements 12. At the line of intersection 14, oneof the elements, 12 for example, is interrupted along its length as itcrosses an element, 10 in this example. The line of intersection 14 isoften referred to as a node or joint. Between adjacent pairs of firstelements 10 and adjacent second elements 12, a cell 11 is formed. Asillustrated, cell 11 is substantially rectangular, but may bedifferently shaped depending upon intended use or other requirements.

FIG. 2 illustrates a composite structure 2 comprising skin or panel 16reinforced or stiffened by elements 10, 12 positioned adjacent to atleast one surface of the panel 16 and arranged to intersect at node orjoint 14.

Composite structures like those illustrated in FIGS. 1 and 2 aretypically fabricated from a number of woven first elements 10, forexample, of sufficient length to span a dimension of the desiredstructure, W in this example. A number of woven second elements 12 arefabricated into geometric shapes to fit between adjacent first elements10. The second elements 12 may be fabricated into L-, C- or Z-shapeswith generally linear horizontal and vertical segments 18 a and 18 b,respectively, as illustrated in FIGS. 3 a-3 c. The generally horizontalsegments 18 a are typically fixed to a portion of the first element, orelements, 10. Nodes or joints 14 are formed at the line of intersectionof elements 10, 12. Elements 10, 12 are processed into compositeassemblies using known processes.

Because elements 10, 12 are structurally separate elements, no fiberscommon to both elements span the node 14. Structurally, the node 14often becomes the weak point in the structure. Loads applied to thecomposite structure 1, 2 or to a element 10, 12 may be transferred alongan element to a node 14. The load-carrying capacity of the node istypically dependent upon the bonding method employed, and usuallylimited by the adhesive system used in the bonding method. Loads inexcess of the load-carrying ability of the node can cause failure of thestructure 1, 2, at the node, often resulting in catastrophic failure.

It is often desirable to provide a node between intersecting elements10, 12 that is capable of transferring greater loads than known nodeconstruction techniques. The instant invention provides a node thatincludes at least one fiber running therethrough. The fiber or fibersrunning through the node increase the load carrying capacity of the nodeby supplementing the load carrying strength of the attachment betweenthe elements.

According to embodiments of the invention, a woven reinforced preform 20comprises a plurality of fabric legs 22-26 woven together as commonlyedgewise joined sheets and intersecting at reinforced node 29 asillustrated in FIG. 4. As illustrated, legs 22-26 are woven together ata line of intersection forming node 29 as part of a fabric and may bewoven using known techniques. Using known weaving techniques, thepreform 20 can be woven to substantially any length, the length beingperpendicular to the view of FIG. 4.

In weaving the reinforced woven preform 20, at least one reinforcingfiber is woven between each of the legs such that each leg shares awoven reinforcing fiber with at least one other leg. For example, leg 22may have at least one common fiber woven with leg 24. Leg 24 may have atleast one common fiber with leg 26, and leg 26 may have at least onecommon fiber with leg 22.

As illustrated, the legs 22-26 comprise major surfaces 22 a, 22 b, 24 a,24 b, 26 a, 26 b which are non-parallel and substantially uniformlytapered along the length, narrowing from the node 24 outward. Inalternate embodiments, the leg surfaces may be substantially parallel,forming legs of uniform thickness along their length, or they may betapered on one side only. The legs 22-26 are illustrated evenly spacedaround node 29 for ease of illustration only. The legs may be positionedat any angular position around the node 29 as may be desirable.

Alternate embodiments may have more that 3 legs radially spaced aroundthe node. A non-limiting, exemplary embodiment of an alternate preformis illustrated in FIG. 5 in which a reinforced woven preform 30comprises 4 legs 32-38, edgewise joined and spaced radially around node39. The legs 32-38 may comprise major surfaces 32 a, 32 b, 34 a, 34 b,36 a, 36 b, 38 a, and 38 b. The legs may be tapered on one or both sidesas illustrated in FIG. 5, or may be uniform in thickness along theirlength as described above.

Embodiments of the present reinforced woven preform may comprise legssimilar to those described above, arranged in pairs positioned radiallyaround the node. Individual legs in a pair may differ from each other,for example, they may be of different dimensions such as thickness T,length in the direction of the node, or width W radially from the node49, as shown in FIG. 6.

As a non-limiting example of a preform with leg pairs, FIG. 6illustrates a preform 40 comprising 6 legs 42, 43, 44, 45, 46, 47arranged as 3 pairs of legs edgewise joined and radially arranged aroundnode 49. Each pair of legs comprises 2 adjacent legs arrangedsubstantially parallel to each other and spaced apart a distance dforming a void. When weaving between leg pairs (42,43), (44,45),(46,47), the reinforcing fiber may weave between adjacent legs, that isa fiber may weave from leg 43 to leg 44, for example. Alternately, areinforcing fiber may weave from one leg, bypass one or more legs, andweave into a subsequent leg. Reinforcing fibers may be woven from oneleg in a pair to another leg in another pair. For example, a reinforcingfiber may weave between a leg in a pair, for example, leg 42 (or 43),may weave with leg 45 (or 46), thus skipping adjacent leg 44. When wovenbetween legs, the reinforcing fiber passes through the node 49.

A similar embodiment is illustrated in FIG. 7 in which a reinforcedpreform 50 comprises 8 edgewise joined legs, comprising 4 pairs of legsspaced apart by a distance d forming a void between the legs, the pairsof legs arranged radially around the node 59. As above, a fiber mayweave from one leg in a pair and weave into a leg in another pair, withthe reinforcing fiber passing through the node 59.

Leg pairs (42,43), (44,45), (46,47) are illustrated in FIGS. 6 and 7 asspaced apart a distance d, forming a void or space between theoppositely facing adjacent major leg surfaces. For ease of illustrationonly, the space as illustrated comprises a flat bottom joined to the legfaces at right angles. It is anticipated that the bottom of the spaceformed between the legs of a pair will not be flat, nor will the bottomand sides join at a sharp angle. In keeping with typical compositepractice, it is anticipated that most inside and outside corners willnot be sharp or square but will be rounded. Corners in the illustrationsare drawn sharp for ease of illustration only.

Exemplary leg major surfaces 42 a, 42 b (FIG. 6) and 51 a, 51 b (FIG. 7)are illustrated as flat and substantially parallel for ease ofillustration only. In the embodiments shown, legs 42-47 (FIG. 6) and51-58 (FIG. 7) are substantially uniform in thickness. As in otherembodiments of the invention, the legs of embodiments illustrated inFIGS. 6 and 7 may comprise non-parallel surfaces and therefore legswhich are tapered along their length.

Preforms may have a linear node along the length of the preform. Thatis, the node may form a straight, or substantially straight, line forthe length of the preform. For example, preforms 20, 30, 40 and 50,shown in end view in FIGS. 4-7, may extend perpendicular to the plane ofthe page for the length of the preform, yielding a linear preform.

Alternately, preforms according to this disclosure may have a portion,or portions, with a curvilinear configuration, or may be entirelycurvilinear over their length. That is, the preform may be formed in, ormay assume, a desired curvilinear configuration, as illustrated bypreform 30 a in FIG. 8. In cross section, the preform 30 a is similar topreform 30 shown in FIG. 5, with 4 elements 32 a-38 a edgewise joinedand spaced radially around node 39 a. A difference is that elements 32a-38 a in FIG. 8 may be woven to accommodate a degree of in-plane orout-of-plane curvature. As illustrated, elements 34 a and 38 a aresubstantially co-planar and are curved within that plane. Elements 32 aand 36 a are substantially co-linear and lie on substantially the samecurved surface, with the elements demonstrating an out-of-planecurvature along the length of the preform.

Reinforced preforms according to embodiments of this invention may beassembled in a variety of ways to form grid-like structures comprisingreinforced nodes. In some embodiments, the reinforced preforms may beassembled to provide reinforced nodes in composite structures, forexample at the intersection of elements. FIG. 9 illustrates anon-limiting example of a reinforced woven preform structure 60according to an embodiment of the invention in which a number ofpreforms 70-75, each comprising 3 woven fabric legs, is assembled in anexemplary combination to form a grid-like composite structure. Differentmanners of combining similar preforms to form a similar structure wouldbe obvious to one of ordinary skill in the art.

FIG. 9 is a plan view of a woven preform structure 60 according to theinvention, with the preforms 70-75 extending perpendicular to the planeof the paper.

According to the non-limiting example of FIG. 9, a woven preformstructure 60 according to the invention may be assembled from reinforcedpreforms 70-75, each composing three legs, or elements, as follows. Afirst preform 70 is arranged such that one leg 70 a is orientedvertically and directed upward, a second leg 70 c is oriented downward,for example to the right of the vertical leg, and the third leg of thetriplet 70 b is oriented downward, to the left as illustrated. A secondpreform 71 is arranged such that a leg 71 b abuts and substantiallyoverlaps leg 70 c on the side of 70 c between 70 a and 70 c (the“outside” of woven preform structure 60). Leg 71 a extends upward and tothe right from the node and leg 71 c is oriented downward from the node,vertically, and generally parallel to leg 70. Preform 72 is arrangedwith a leg 72 b oriented substantially vertically, abutting andsubstantially overlapping leg 71 c to the side of 71 c between leg 71 band 71 c (the “inside” of the structure 60).

Preform 73 is arranged with leg 73 a oriented vertically downward,substantially co-planar with leg 70 a. Leg 73 c is oriented upward tothe right, abutting and substantially overlapping leg 72 c, to the sideof 72 c forming the inside of the structure. Leg 73 b is oriented upwardto the left. Preform 74 is arranged similar to preform 72, offset to theleft of 72. Leg 74 a is oriented vertically upward, leg 74 c is orienteddownward to the right, abutting and substantially overlapping leg 73 bto the inside of the structure. Leg 74 b is oriented downward to theleft. Preform 75 is arranged in a manner similar to that of preform 71,offset to the left of preform 71. Leg 75 b is oriented verticallydownward abutting and substantially overlapping leg 74 a to the outsideof the structure. Leg 75 c is oriented upward toward the right abuttingand substantially overlapping leg 70 b. Leg 75 a is oriented upward tothe left.

Thus arranged, preforms 70-75 form a woven preform structure 60comprising a substantially hexagonal cell 13. It would be obvious to oneof ordinary skill in the art that the single cell 13 illustrated in FIG.9 could be expanded into a grid-like structure by combining additionalpreforms, similar to 70-75, with the illustrated preform structure byoverlapping and abutting preform legs in a similar manner, formingadditional hexagonal cells. As discussed above, the structure may befurther processed to form a composite structure using any of the knownmethods.

The woven fabric legs 70 a-75 c in FIG. 9 are shown as line segments forease of illustration only. In such a structure, the legs of each wovenpreform would necessarily have a thickness. It is anticipated that wovenfabric legs 70 a-75 c may have a varying thickness along the length ofat least some of the legs. For example, the legs 70 a-75 c of the wovenpreform of FIG. 9 may have a uniformly varying leg thickness similar tothat illustrated in FIG. 4. Alternately, the legs of the preformscomprising the structure 60 of FIG. 9 may also be of uniform thickness.

Overlapping legs, for example legs 70 c and 71 b, may form a single lapshear joint when the structure 60 is cured into a composite structure.Legs having varying thickness, when overlapped, may form a leg having auniform, or substantially uniform, thickness along its length. Asillustrated in FIG. 9, according to one embodiment of the invention, thelegs 70 a-75 c of woven preforms 70-75 are substantially the same lengthsuch that overlapping legs may be substantially coextensive. In someembodiments, overlapping legs may not be the same length. In addition,legs 70 a-75 c may differ in depth, taken perpendicular to the view ofFIG. 9.

In FIG. 10, reinforced preforms 80, 81, 82, and 83, may be assembled toform a woven preform structure 62 according to another embodiment of theinvention. Preforms 80-83 comprise woven fabric legs 80 a-83 d. As withthe embodiment of FIG. 9, legs 80 a-83 d of the preform structure 62 ofFIG. 10 are illustrated using line segments for ease of illustrationonly. In such a structure, the legs of each woven preform wouldnecessarily have a thickness. It is anticipated that woven fabric legs80 a-83 d may have a varying thickness along the length of at least someof the legs. For example, the legs 80 a-83 d of the woven preform ofFIG. 10 may have a uniformly varying leg thickness similar to thatillustrated in FIG. 5.

According to the non-limiting example of FIG. 10, a woven preformstructure 62 according to the invention may be assembled from reinforcedpreforms 80-83, each composing four legs, as follows. A first preform 80is arranged with a pair of legs 80 a and 80 c arranged vertically andcoplanar, with legs 80 b and 80 d coplanar with each other andperpendicular to 80 a, 80 c. That is, 80 b and 80 d are horizontallyoriented, with 80 b to the right of 80 a, 80 c. Preform 81 may bearranged such that legs 81 a and 81 c are coplanar and verticallyoriented such that 81 a, 81 c are parallel to and offset to the rightfrom 80 a, 80 b. Coplanar legs 81 b and 81 d are horizontally orientedwith leg 81 d abutting and substantially overlapping leg 80 b to theside opposite leg 80 a (the “inside” of woven preform structure 62).Preforms 83 and 82 are arranged similarly to preforms 80 and 81,respectively, with 83 and 82 located below 80, 81. Vertical legs 82 aand 82 c are coplanar and oriented with leg 82 a abutting andsubstantially overlapping leg 81 c to the inside of the structure.Vertical legs 83 a and 83 c are coplanar and oriented with leg 83 aabutting and substantially overlapping leg 80 c to the outside of thestructure. Horizontal legs 82 b and 82 d are coplanar and parallel tolegs 80 b, 80 d, 81 b, 81 d. Horizontal legs 83 b and 83 d are coplanarand parallel to legs 80 b, 80 d, 81 b, 81 d, with leg 83 b abutting andsubstantially overlapping leg 82 d toward the inside of the structure.

Overlapping legs, for example legs 80 b and 81 d, may form a single lapshear joint when the structure 62 is formed into a composite structure.Legs having varying thickness, when overlapped, may form a leg having auniform, or substantially uniform, thickness along its length. Asillustrated in FIG. 10, according to one embodiment of the invention,the legs 80 a-83 d of woven preforms 80-83 are substantially the samelength such that overlapping legs may be substantially coextensive. Insome embodiments, overlapping legs may not be the same length. Inaddition, legs 80 a-83 d may differ in depth, taken perpendicular to theview of FIG. 9.

Thus arranged as in FIG. 10, preforms 80-83 form a woven preformstructure 62 comprising substantially rectangular cell 11. It would beobvious to one of ordinary skill in the art that the single cell 11illustrated in FIG. 10 could be expanded into a grid-like structure bycombining additional preforms, similar to 80-83, with the illustratedpreform structure by overlapping and abutting preform legs in a similarmanner. As discussed above, the preform structure 62 may be furtherprocessed to form a composite structure using any of the known methods.

Curvilinear preforms may be similarly assembled to form similarstructures as illustrated in FIG. 10. Curvilinear preforms can beassembled, for example, as illustrated in FIG. 11, in which two preforms30 b and 30 c, similar to preform 30 a of FIG. 8, are assembled in anexemplary configuration prior to being formed into a compositestructure. Preforms 30 b and 30 c have the same, or substantially thesame, curvature such that elements or legs 34 b and 38 c overlap andremain substantially parallel and abutting over their lengths, which mayor may not be coextensive. Preforms 30 b and 30 c may be woven such thatthe lengths of preform are positionable in the desired curvedorientation and remain so configured without the need for positioningmeans prior to being formed into a composite structure.

It would be obvious to one of ordinary skill in the art to combineadditional preforms, similar to 30 b and 30 c to form a larger grid-likestructure. One non-limiting example of such a structure 100 isillustrated in FIG. 13. An exemplary use for structure 100 may includeuse as a thrust reverser or cascade, commonly used to direct the flow ofair around an aircraft turbine engine. Other structures made in asimilar fashion and/or other uses for the exemplary structure 100 wouldbe obvious to one of skill in the art.

In other embodiments, preforms may be woven in an easily fabricatedshape, for example as linear preforms, and placed in a suitably shapedmold to retain the preform in the desired final shape. One non-limitingexample of a mold configured to retain a preform in the desired shape isillustrated in FIG. 13. As shown, a cruciform-shaped preform 32 d isplaced in a cavity formed between 4 mold elements 102-108. The moldelements are configured in the desired net shape, or near net shape, ofthe final composite structure using conventional forming means. Underproper processing conditions in a molding apparatus, preform 32 d may beprocessed into a composite structure having the desired shape.

FIG. 14 illustrates an example of a formed composite structure 101produced by the mold configuration illustrated in FIG. 13 subjected toproper processing conditions.

Larger structures could be formed by placing multiple preforms andmultiple sets of mold elements 102-108 adjacent to the preforms and moldelements of FIG. 13 such that at least one leg of each preform overlapsand is held in a abutting relationship with at least one leg of anadjacent preform and processed to form a composite structure.

Alternately, multiple structures 101 could be formed and assembled withoverlapping elements using known techniques to form a larger structure.

Reinforced woven preform structures according to the invention may beuseful in fabricating reinforced nodes between intersecting elements. Ina further embodiment according to the invention, reinforced wovenpreform 90, similar to that illustrated in FIG. 7, may be assembled withsecondary elements 92, 94, 96, and 98 to form a preform structure 64 asshown in FIG. 15. As illustrated, first ends of secondary elements 92-98may be inserted at least partially into the space between substantiallyparallel leg pairs (51, 52), (53, 54), (55, 56), (57, 58), in whichopposite facing leg surfaces in a pair (for example 51 b and 52 b inFIG. 7) are spaced apart a distance, d. The space, d, may be configuredto closely engage the element inserted therein. In some embodiments, thespace, d, may provide some clearance between the element and theopposite facing leg surfaces to accept, for example, an adhesive.

Woven preform 90 can be used to form a reinforced node at theintersection of elements in a stiffened panel or skin. As illustrated inFIG. 2, intersecting elements 10 and 12 form a node 14 at the line ofintersection. Woven preform 90 may be placed at the node 14 with legpairs (51, 52) and (55, 56) accepting end portions of interruptedelement 12 and leg pairs (53, 54) and (57, 58) accepting end portions ofinterrupted element 10.

Woven preform structure 64 may be converted to a reinforced compositestructure using methods discussed above.

The woven preform structure 64 is illustrated in FIG. 15 as a singlenode joining 4 elements for ease of illustration only. Elements 92-98are identified as secondary elements to distinguish them from otherelements in the preform. It would be obvious to one of ordinary skill inthe art that the preform structure 64 may be repeated using additionalwoven preforms 90 at second ends of secondary elements 92-98, along withadditional elements (not shown) to form a grid like structure comprisingsubstantially rectangular cells 11, similar to that illustrated in FIG.10.

One of ordinary skill in the art would recognize that grid-likestructures comprising cells of other shapes may be achieved fromdifferently configured woven preforms. For example, a woven preform 40in FIG. 6 employed in a similar fashion as described above to joinelements, could produce a woven preform structure comprisingsubstantially hexagonal cells similar to cell 13 in FIG. 9.

Alternately, “hybrid” woven preforms may be formed with at least someelements arranged in pairs and others arranged singularly. As anon-limiting example, one embodiment according to the invention isillustrated in FIG. 16. Woven preform 110 has four consecutive elementsarranged as two pairs of elements (111,112), (113,114), and two elements(115 and 116) arranged singularly. For ease of illustration, the node119 is shown as a darkened circle and the 6 elements 111-116 are show aslines, representing the configurations of elements as discussed above,that is, elements having parallel or non-parallel major surfaces.

FIG. 17 represents one non-limiting example of a composite structurecomprised of the hybrid preforms 110 of FIG. 16. As illustrated, acomposite structure 120 is comprised of 4 hybrid preforms, assembledsuch that each singular element 115 and 116 is accepted within the voidformed between pairs of elements (111,112) and (113,114). This patterncan be continued to form structures larger than the 3×3 gridillustrated. Hybrid preforms having other arrangements of singularelements and pairs of elements is anticipated, as are hybrid preformswith elements arranged in groups of more than 2. For example, somehybrid preforms may comprise groupings of elements in twos, threes, ormore, with or without singular elements. In addition to the generallycruciform configuration shown in FIG. 16, hybrid preforms may befabricated in other configurations such as the triad configuration ofFIGS. 4 and 6, with or without singular elements.

In non-limiting, exemplary embodiments of the inventive method,grid-like structures and reinforced panels or skins with reinforcednodes can be fabricated in a more economical process than previouslyknown. The method is suitable for use with straight and shaped preforms,that is, with preforms as discussed in the embodiments above in whichthe length in the longitudinal direction may be linear or curvilinear.The process may include a mold or form, generally, tooling shaped andconfigured to correspond with the desired shape of the finished product.

Preforms according to the non-limiting exemplary methods of producing agrid-like structure or reinforced panel are, in general, fabricated asfollows. The method presented is for a cruciform shaped preform,recognizing that other shapes having fewer or more elements may be usedin a similar method. A cruciform grid-like structure may be representedby the exemplary reinforced woven preform structure 62 of FIG. 10. Apreform structure fabricated with preforms having three elements may berepresented by the exemplary reinforced woven preform structure 60 ofFIG. 9.

As an exemplary first step, a cruciform preform (30 or 80) is woven fromfibers that have a coating or comprise a component capable of being heatset. Alternately, the preform may be coated or processed at apost-weaving step with a suitable coating. Non-limiting examples ofappropriate coatings suitable for heat setting include sizing ortackifiers. In the alternative, preforms may pre-impregnated with amatrix or resin material after weaving.

Tooling comprising a mold cavity or cavities with shapes, contours anddimensions corresponding to the desired final shape is fabricated. Themold will typically comprise a repeated pattern of shapes correspondingto the desired size and shape of the grid-like structure. The preformsmay be received within the mold in such a way that at least some legs ofadjacent preforms abut each other and overlap at least some amount. FIG.10 illustrates cruciform preforms arranged such that the legs ofadjacent preforms overlap essentially completely. Other embodiments mayprovide different degrees of overlap depending on requirements. The moldis capable of opening to allow insertion of the appropriate preforms,and closing to seal the preforms within cavities as known in the art.

Preforms may be pre-cut to the correct length and placed in the mold, oroversized preforms may be placed in the mold and trimmed to size in themold. After each mold cavity has received a preform insert and any othermaterials to be included in the composite grid-like structure, the moldis closed, sealing the cavities in which the preforms are located forprocessing into a composite structure.

The mold elements, inserted preforms, and any additional materialsplaced in the mold may be pre-heated in the mold prior to furtherprocessing. Under appropriate conditions, a resin or matrix material isinjected under suitable pressure and temperature to fill the mold and toform the grid-like structure. After proper processing, the grid-likestructure may be removed from the mold for post mold processing asnecessary or desired.

Having thus described in detail various embodiments of the presentinvention, it is to be understood that the invention defined by theabove paragraphs is not to be limited to particular details set forth inthe above description as many apparent variations thereof are possiblewithout departing from the spirit or scope of the present invention.

1. A reinforced preform comprising: a plurality of commonly woven fabricelements edgewise joined and radially extending from a common node,wherein at least one reinforcing fiber from each of the plurality ofelements is woven through the node and into at least one other of theplurality of elements.
 2. The reinforced preform of claim 1 wherein atleast one of the fabric elements comprise generally parallel majorsurfaces.
 3. The reinforced preform of claim 1 wherein at least one ofthe fabric elements comprise at least one major surface tapering fromthe common node to the end of the element.
 4. The reinforced preform ofclaim 1 wherein the elements further comprise major surfaces; andwherein at least some of the plurality of elements are arranged in pairsof adjacent elements such that opposite facing adjacent major surfacesare spaced apart a distance and form a void therebetween.
 5. A compositestructure comprising: a plurality of preforms, each preform comprising aplurality of commonly woven fabric elements edgewise joined and radiallyextending from a common node, at least one reinforcing fiber from eachof the plurality of elements woven through the node and into at leastone other of the plurality of elements wherein each of the plurality ofpreforms includes a longitudinal axis, the axes of the plurality ofpreforms aligned generally parallel in a grid-like pattern; and a firstend of a first woven fabric element of a first of the plurality ofpreforms overlaps and abuts at least a second woven fabric element of asecond of the plurality of preforms.
 6. A composite structurecomprising: a plurality of preforms, each comprising a plurality ofcommonly woven fabric elements edgewise joined and radially extendingfrom a common node, the fabric elements comprising major surfaces andhaving at least one reinforcing fiber from each of the plurality ofelements woven through the node and into at least one other of theplurality of fabric elements; wherein a first of the plurality ofpreforms comprises adjacent woven fabric elements arranged in pairs suchthat opposite facing adjacent major surfaces are spaced apart a distanceand form a first void therebetween; and the structure further comprisinga secondary element, a first end of which is at least partially receivedwithin the first void.
 7. The composite structure of claim 6 furthercomprising: a second preform of the plurality of preforms comprisingadjacent elements arranged in pairs such that opposite facing adjacentmajor surfaces are spaced apart a distance and form a void therebetween;and a second end of the secondary element is at least partially receivedwithin the second void formed in the second preform, at least partiallyoverlapping and abutting at least one of the opposite facing adjacentmajor surfaces thereof.
 8. The composite structure of claim 7 whereinthe secondary element comprises a woven fabric.
 9. A method of forming areinforced composite structure comprising the following steps:fabricating a first reinforced preform comprising a plurality ofcommonly woven fabric elements edgewise joined and radially extendingfrom a common node wherein at least one reinforcing fiber from each ofthe plurality of elements is woven through the node and into at leastone other of the plurality of elements; fabricating a second preformcomprising at least one secondary element; positioning at least aportion of the secondary element adjacent to at least a portion of thefirst woven preform to form a preform assembly; processing the preformassembly to form a composite structure.
 10. The method according toclaim 9 wherein: the fabric elements of the first reinforced preformcomprise major surfaces; the second preform further comprises aplurality of secondary elements, the secondary elements comprising majorsurfaces; and the first reinforced preform and the second preform eachhaving longitudinal axes, wherein the method further comprises:arranging the first reinforced preform and the second preform with theirlongitudinal axes generally parallel; and positioning the firstreinforced preform and the second preform such that a portion of atleast one of the major surfaces of the first reinforced preform at leastpartially overlaps and abuts a portion of at least one of the majorsurfaces of a secondary element of the second preform.
 11. The methodaccording to claim 10 further comprising: arranging at least some of thefabric elements of the first reinforced preform in pairs of adjacentelements such that opposite facing adjacent major surfaces are spacedapart a distance and form a void therebetween; and positioning at leasta portion of a first end of one of the plurality of secondary elementswithin one of the voids formed in the first reinforced preform,overlapping and abutting at least a portion of one of the oppositefacing adjacent major surfaces thereof.
 12. The method of claim 11further comprising: fabricating a second reinforced preform comprising aplurality of commonly woven fabric elements edgewise joined and radiallyextending from a common node, the fabric elements comprising majorsurfaces and having at least one reinforcing fiber from each of theplurality of elements woven through the node and into at least one otherof the plurality of elements; arranging at least some of the fabricelements of the second reinforced preform in pairs of adjacent elementssuch that opposite facing adjacent major surfaces are spaced apart adistance and form a void therebetween; and positioning a second end ofthe secondary element such that it is at least partially received in oneof the voids formed in the second reinforced preform, overlapping andabutting at least a portion of one of the opposite facing adjacent majorsurfaces thereof.